Dehydrogenation of hydrocarbons in an electric field

ABSTRACT

An improvement in a process for the catalytic dehydrogenation of dehydrogenatable hydrocarbon feedstocks to form compounds having a higher carbon to hydrogen ratio is disclosed. The process is carried out while subjecting the solid catalyst, which contains a group VIb metal oxide, to a high-voltage electrical field of at least about 1000 volts/cm.

United States Patent Inventors Leonard D. Krenzke Riverdale; Glenn 0.Michaels, South Holland, both 01' Ill. App]. No. 853,033 Filed Aug. 26,1969 Patented Oct. 26, 1971 Assignee Atlantic Richfield Company NewYork, N.Y.

DEHYDROGENATION OF HYDROCARBONS llN AN ELECTRIC FIELD 11 Claims, 1Drawing Fig.

11.8. C1 204/168, 204/312 Int. Cl. C07b 29/06, B011: 1/00 Field ofSearch 204/168,

Primary Examiner-F. C. Edmundson Attorney-Morton, Bernard, Brown,Roberts & Sutherland ABSTRACT: An improvement in a process for thecatalytic dehydrogenation of dehydrogenatable hydrocarbon feedstocks toform compounds having a higher carbon to hydrogen ratio is disclosed.The process is carried out while subjecting the solid catalyst, whichcontains a group Vlb metal oxide, to a high-voltage electrical field ofat least about 1000 volts/cm.

PATENTED E 2 3,616,381

INVEN'I'OR LEONARD D. KRENZKE 8 GLENN O. MICHAELS 774 Yam/(nu y ADEHYDROGENATION F HYDROCARBONS IN AN ELECTRIC FIELD This inventionrelates to a process for the catalytic dehydrogenation ofdehydrogenatable hydrocarbon feedstocks to form products having a highercarbon to hydrogen ratio. More particularly, this invention relates to aprocess for the dehydrogenation of such hydrocarbons wherein thefeedstock is contacted with a dehydrogenation catalyst containing agroup Vlb metal oxide at a dehydrogenation temperature of from about 900to l250 F., and while the catalyst is subjected to a high-voltageelectrical field.

Dehydrogenation catalysts having one or more group Vlb metal (i.e.,chromium, molybdenum and tungsten) oxides on a solid support have beenused to dehydrogenate hydrocarbons to more olefnic and/or diolefinicstructures. Chromia supported by alumina is the most frequently usedcatalyst of this type, with the chromia being present in a minor amountof from about I to 40 weight percent of the catalyst. Quite frequently,dehydrogenation will be carried out with a catalyst containing fromabout percent to percent C50,, carried on a high surface area supportsuch as activated alumina. Commonly, an alkali metal oxide is present inthe catalyst in a small amount, of say, 0.1 to 4 weight percent,sufficient to counteract the acid sites on the catalyst to minimizecracking and isomerization reactions. The catalyst further can containminor amounts of other components such as metal oxides, e.g. zinc oxideor magnesium oxide. These catalysts have been used in such processes asthe production of butenes and butadiene from n-butane, isoprene fromisopentane or isoamylene, styrene from ethyl benzene and a number ofsimilar dehydrogenation reactions.

The catalyst can, for example, contain Cr,0;,, Mg0, alkali metal oxideand alumina as is taught in U.S. Pat. No. 3,363,023. As is disclosedtherein, the dehydrogenation catalyst may contain at least about l or 5to 40 weight percent Cr tl about 1 to 40 weight percent Mg0, about 0.1to 4 weight percent alkali metal oxide, and the balance alumina. TheMgfl can be in oxide form or chemically combined with the alumina base,as for example, a magnesium aluminate spinel. Rather than magnesiumoxide, the catalyst can contain,

in addition to C50,, alkali metal oxide and alumina, zinc oxide in aminor amount of, say, about 5 to 40 weight percent which can be providedin oxide form or chemically combined with the alumina base, as forexample, a zinc aluminate spinel.

The use of these types of catalysts is also known in thedehydrocyclization of aliphatic hydrocarbons to form aromatichydrocarbons, see, for example, U.S. Pat. Nos. 2,271,751; 2,357,271; and2,378,209. This process, which combines dehydrogenation and cyclization,is usually effected at a temperature of from about 900 to l250 F. Withthe hydrocarbons in the vapor phase and at a pressure fromsubatmospheric up to about 2 atmospheres or more.

In accordance with the process of this invention, the dehydrogenation ofa hydrocarbon feedstock is performed by contacting the feedstock with adehydrogenation catalyst of the foregoing described types, while thecatalyst is subjected to a high-voltage electrical field sufficient toincrease the yield of the dehydrogenated product. The electrical filedcan have a strength of above about 1,000 or 5,000 volts/centimeter up toa strength just below the arcing voltage. Preferably, the voltage isfrom about 8,000 or 12,000 volts/centimeter to about 25,000volts/centimeter or more. The high-voltage electrical field can beapplied using AC, DC or pulsating DC current.

The dehydrogenation process is conducted in the vapor phase at anelevated temperature, for instance, about 900 to 1,250 F., preferablyl,000 to l,l50 F., and a hydrocarbon pressure of up to about 2atmospheres or more. Generally, increased selectivities are obtained athydrocarbon pressures below atmospheric, say down to about 0.05atmosphere or below, with a hydrocarbon pressure of about 0.1 to 0.5atmosphere being preferred for economic reasons. If desired, an inertdiluent or vacuum can be employed to reduce the hydrocarbon partialpressure of the hydrocarbon feed. Various essentially inert, gaseousdiluents can be employed but it is preferred to use nitrogen, hydrogenor methane. The inert gas is usually present in an amount of about 0.5to 50 moles, preferably 5 to 25 moles, per mole of hydrocarbon feed. Thecontact time or weight hourly space velocity can vary, depending on thetemperature and pressure employed but will generally range from about0.05 to 5, preferably 0.1 to 2 WHSV. The catalyst preferably contains aminor amount of chromia supported on an alumina base.

The catalyst support is generally a porous solid oxide and alumina ispreferably the major component of the catalyst. Activated orgamma-family aluminas can be employed such as those derived bycalcination of amorphous hydrous alumina, alumina monohydrate, aluminatrihydrate or their mixtures, at elevated temperatures of, for instance,about 750 to l,S00 F., preferably about 850 to 1,400 F. Advantageously,the alumina precursor may be a mixture predominating, for instance,about 65 to percent by weight, in one or more of the aluminatrihydrates: bayerite, nordstrandite or gibbsite, and about 5 to 35percent by weight alumina monohydrate (boehmite), amorphous hydrousalumina or their mixtures. Catalyst bases of this type are disclosed inU.S. Pat. Nos. 2,838,444 and 2,838,445. The alumina base may alsocontain small amounts of other solid oxides. The preparation of a basecontaining a magnesium aluminate spinal or zinc aluminate spinel isknown in the art. For example, a preferred method of obtaining asuitable magnesium aluminate spinel is described in U.S. Pat No.2,992,191 to Henry Erickson. A preferred method of obtaining a zincaluminate spinel is described in U.S. Pat. application Ser. No.550,1!76, filed May l6, 1966 now U.S. Pat. No. 3,470,262.

impregnation of the alumina base with the catalytically active metalcomponents can be by known methods. Forinstance, the base can be mixedwith an aqueous solution of a water-soluble salt of the catalyticallyactive components of the catalyst to absorb all or part of the solutionin the support which is then dried and calcined, for instance at thetemperatures noted above, to give an active catalyst. Alternatively, theactive components can be precipitated on the support throughneutralization of a slurry of the support and water-soluble compounds ofthe catalytically active metals and then drying and calcining.Calcination activates the catalyst and, if not already present as theoxide, may convert the catalytically active metal components to theiroxide form. The impregnation with the catalytically active componentscan be done separately or simultaneously.

If desired, the alumina base can be ground before addition of thecatalytic metals and the resulting material formed, if desired, intolarger particles, impregnated and dried before effecting the calcinationwhich gives the final catalyst. Alternatively the base particles can bedirectly impregnated, dried and calcined; or directly impregnated,ground and formed into shaped particles by tabletting or extrusion andthen calcined. It is preferred to calcine the alumina prior to additionof the catalytically active components. After the catalytically activecomponents are added to the base, the resulting catalyst compositionscan be activated by drying and calcination, for instance, at thetemperatures noted above.

The hydrocarbon feeds of the present invention are dehydrogenatablehydrocarbons of 2 to about 20 or more carbon atoms, often of about 4 to5 to 12 carbon atoms. The feeds are usually nonacetylenic and often aresaturated or monoolefinically unsaturated hydrocarbons. Whether thereaction or principal reaction occurring is a straight dehydrogenationas opposed to dehydrocyclization. will be dependent in large part uponthe feed selected. Both dehydrogenation to create one or two doublebond-containing products and dehydrocyclization may occur with somefeeds.

Should noncyclic monoolefins and/or diolefins be the desired productsthe preferred feeds are aliphatic hydrocarbons of 4 to 6 carbon atomsalthough as aforementioned, they can have up to about 12 or 20 or morecarbon atoms. The feeds can be unsaturated but the preferred feeds arethe normal and branched chain parafiins, including the cyclic paraffinssuch as cyclopentane and cyclohexane. Equally suitable are aromaticfeeds containing one or more dehydrogenatable aliphatic hydrocarbongroups, e.g. a lower alkyl group say of l to 4 carbon atoms as in thecase of ethylbenzene. Among the unsaturated feeds which can be used arethe olefins of the C, to C range which may undergo dehydrogenation toyield .W an-.

The invention will be further described with reference to the appendeddrawing in which The FIGURE is a schematic representation of one mode ofthe invention.

The FIGURE shows a reactor cylindrical vessel 1 made of a suitablenonconducting material such as glass with an inlet 2 and an outlet 3.Located in the lower part of the reactor vessel 1 is a catalyst bed 4composed of a Group Vlb metal oxide supported on an alumina base. Thecatalyst bed 4 is supported on a layer 5 of tabular alumina. The reactorvessel 1 is located within heating means 6 which serve to heat thereactor vessel and contents to a desired temperature. The reactor inlet2 connects with a tube 7 also made of a suitable nonconducting materialsuch as glass, which is located within the reactor vessel 1, preferablyat the center of the vessel, and which extends down to the bottom of thecatalyst bed 4. An electrode wire 8 made of a metal such as stainlesssteel is located within tube 7 nd also extends to the bottom of catalystbed 4. A second electrode wire 9 enters the reactor vessel ll throughthe stopper l0 which seals the top of the reactor vessel and extends ofthe following composition:

Wt. propane 0.02 isobutane 99.8 n -butane 0.17

Data on the effect of an electric field on the conversion of isobutaneis shown in table l below. The positive potential was applied toelectrode 9. The samples taken from the runs using the regeneratedcatalyst and while the potential was applied, e.g., samples 21, 23, and25, were taken after the oltage had been applied for about 15 minutesand while the voltage was being applied. Similarly, the samples takenwithout the potential applied other than the first sample afterregeneration, e.g., samples 19, 22 and 24, were taken about 15 minutesafter the potential was taken ofi' the catalyst.

TABLE 1 Run Number Conditions:

Temperature, F 1, 050 1, 050 1, 050 1, 050 1, 050 1, 050 l, 050 1.050WHSV 0.8 0. 8 1. 00 1.07 1. 07 1.07 l. 07 1.07 Pressure Sampling time(min. 10 25 10 75 90 117 Applied potential (D volts 10, 000 0 0 5,000 010,000 0 15,000 Analysis of Etfluent, wt. percent:

Hydrogen, methane, ethane and ethene... 23 .10 .36

Propane lsobutene and n-but-ene. trans-Butene.

B utadiene Estimated conversion oi ioifw'tfbini i The catalyst wasregenerated with air between Runs 19 and 20.

2 Atmospheric. 3 Trace.

downwardly into the catalyst bed 4. The second electrode 9 is preferablyformed in a spiral in the catalyst bed 4 around the tube 7 and extendsto about the bottom of the catalyst bed 4.

In operation, the reactor vessel 1 (with the catalyst bed 4, tube 7 andelectrode wires 8 and 9 therein) is heated by heating means 6 to atemperature of about 900 to l,250 F feed is introduced through inlet 2and a high-voltage electrical source (not shown) is applied between theelectrodes 8 and 9. The products are collected from the outlet 3.

The following example further illustrates the process of the instantinvention.

EXAMPLE The reactor vessel of the FIGURE was filled with 7 grams of aregenerated chromia-alumina dehydrogenation catalyst containing about 20weight percent chromia and about 0.4 weight percent sodium oxide, whichhad been aged 50 days in a commercial butane dehydrogenation unit. Thecatalyst was ground to 8-14 mesh and dispersed in the reactor so that itcompletely covered the spiral of electrode 9. Feed was introduced to thecatalyst bed through the tube 7 around electrode 8. The products werecollected by conventional means. The conver sion of the feed wasestimated from gas chromatographic analysis of the effluent taken atintervals throughout a run.

As may be noted from the table, the conversion of isobutane increasedwith the application of an electrical field. In particular, theestimated conversion after 10 minutes with an applied potential of10,000 volts (Run No. 18) was 23.3 percent while the estimatedconversion after 10 minutes of the regenerated catalyst with noelectrical field was 15.0 percent. This represents an increase inconversion of about 55 percent. With no voltage applied, conversiondropped from 15.0 percent at t= 10 min. to 9.25 percent at the end ofminutes. With 5,000 volts applied, a small difference in the expectedactivity was noted. However, with the application of 10,000 volts at t=75 min. the conversion was 13.0 percent or about 3 percent above andabout 30 percent greater than the expected value and with 15,000 volts(t=l 15 min.) conversion increased to 30.5 percent. The latterconversion is over 3 times the expected result with no applied voltage.

Although the above runs were made with a direct current source, thepotential can be applied with an alternating current source or apulsating direct current source. The exact mechanism for the enhancedresults produced by the application of the electric field is not knownbut the effects appear similar to those produced in a catalyst by theintroduction of a promoter. However, once a promoter is added to acatalyst, the results are more or less permanent since the promotercannot be removed easily or rapidly. The advantage of using anelectrical field to achieve these increased yields is apparent since itcan be removed easily.

IT IS CLAIMED:

1. in a method for the conversion of hydrocarbon feedstocks to increasethe ratio wherein the feedstock is contacted at a temperature of fromabout 900 to l,250 F. in the vapor phase over a dehydrogenation catalystcontaining a group Vlb metal oxide supported on a solid base, theimprovement wherein the catalyst is subjected to a high-voltageelectrical field of from about 8,000 volts/cm. sufficient to increasethe yield of dehydrogenated product but below the arcing voltage.

2. The method of claim 1 wherein the feedstock is isobutane.

3 The method of claim 1 wherein the catalyst has a minor amount ofchromia supported on alumina.

4. The method of claim 1 wherein the dehydrogenation is carried out at ahydrocarbon pressure of from about 0.05 to 2 atmospheres.

dehydrogenatable carbon to hydrogen 5. The method of claim 4 wherein thetemperature is from about l,00O to l,l50 F., and the pressure is fromabout 0.! to 0.5 atmosphere.

6. The method of claim 1 wherein the electric field is from about 8,000to 25,000 volts/centimeter.

7. The method of claim 1 wherein the catalyst contains 1 to 40 weightpercent chromia, a small amount of an alkali metal oxide and the base isalumina.

8. The method of claim 6 wherein the dehydrogenation is carried out at ahydrocarbon pressure of from about 0.05 to 2 atmospheres.

9. The method of claim 8 wherein the temperature is from about 1,000 tol,l50 F., and the pressure is from about 0.1 to 0.5 atmosphere.

10. The method of claim 9 wherein the catalyst contains l to 40 weightpercent chromia, a small amount of an alkali metal oxide and the base isalumina.

11; The method of claim 10 wherein the feedstock is isobutane.

# t i U II

2. The method of claim 1 wherein the feedstock is isobutane. 3 Themethod of claim 1 wherein the catalyst has a minor amount of chromiasupported on alumina.
 4. The method of claim 1 wherein thedehydrogenation is carried out at a hydrocarbon pressure of from about0.05 to 2 atmospheres.
 5. The method of claim 4 wherein the temperatureis from about 1,000* to 1,150* F., and the pressure is from about 0.1 to0.5 atmosphere.
 6. The method of claim 1 wherein the electric field isfrom about 8,000 to 25,000 volts/centimeter.
 7. The method of claim 1wherein the catalyst contains 1 to 40 weight percent chromia, a smallamount of an alkali metal oxide and the base is alumina.
 8. The methodof claim 6 wherein the dehydrogenation is carried out at a hydrocarbonpressure of from about 0.05 to 2 atmospheres.
 9. The method of claim 8wherein the temperature is from about 1,000 to 1,150* F., and thepressure is from about 0.1 to 0.5 atmosphere.
 10. The method of claim 9wherein the catalyst contains 1 to 40 weight percent chromia, a smallamount of an alkali metal oxide and the base is alumina.
 11. The methodof claim 10 wherein the feedstock is isobutane.